Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

944
FXUS63 KLOT 041222
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
622 AM CST Wed Mar 4 2026

.KEY MESSAGES...

- Dense fog is expected through mid morning across portions of
  northern Illinois.

- Additional periods of dense fog may impact portions of the
  area tonight through Friday morning.

- Waves of showers and a few thunderstorms will be possible
  tonight into Thursday (along with drizzle at times).

- Friday will be windy and unseasonably warm, with a period of
  showers and embedded thunderstorms during the daytime hours
  and then more widespread showers and scattered storms late
  Friday night into early Saturday. Some of these storms may be
  strong to even severe, though confidence is low.

&&

.DISCUSSION...
Issued at 343 AM CST Wed Mar 4 2026

Through Thursday:

Fog has expanded in coverage across northern Illinois early
this morning where a Dense Fog Advisory is currently in effect
through 9 AM CST. There is a mid-level cloud feature slowly
lifting north across the dense fog area that has allowed for
some improvement in the visibility along the southern periphery,
but this has not been consistently for all areas. Thus, suspect
at least locally dense fog will persist into mid-morning,
especially near the Wisconsin line. Temperatures are near and
below freezing across far northeast Illinois which could lead to
patchy slick spots developing on untreated surfaces.

Confidence in temperatures trends is low owing to uncertainty in
how long the fog persists this morning along with any remaining
low clouds. Current forecast favors some erosion of this cloud
layer (which may be too optimistic), and allow temperatures to
still warm into the mid-upper 40s inland of Lake Michigan.
However, if low clouds remain overhead for most of the day,
temperatures would struggle to warm out of the mid 30s near the
lakeshore and lower 40s farther inland north of I-80. There may
be enough warm air advection south of I-80 (ESE winds) to allow
temperatures to still warm into the mid to upper 40s amidst
overcast skies.

Dry conditions are favored for most of the area through this at
least mid-afternoon. There is a low chance of light
showers and/or drizzle to lift north across part of the area
late afternoon into the evening. Hi-res guidance (RAP/HRRR) is
most bullish on this in depicting this though there remain
questions as to whether we saturate sufficiently for
precipitation to occur. An increase in precipitation chances
during this timeframe may be needed with later updates if
confidence increases.

Waves of showers are then expected to lift across the region
tonight into Thursday though there remains a lot of variability
in the coverage and exact timing of showers here locally. Opted
to maintain a blended approach to precipitation chances which
has shower coverage increasing from south to north through the
overnight hours then ending from west to east into the
afternoon on Thursday as the center of the surface low moves
across the area. While instability looks rather meager during
this timeframe (MUCAPE < 500 J/kg), a few rumbles of thunder
can`t be ruled out with this activity.

This pattern remains favorable periods of fog as low-level
moisture increases across a still cold Lake Michigan. Given
onshore flow is expected the next few days fog will likely
advect inland at times across northern Illinois, some of which
could be dense. Have maintained and expanded fog coverage
wording in the official forecast from late tonight through the
day on Thursday to account for this.

Petr


Thursday Night:

The main concern Thursday night into Friday morning is fog
trends, with the synoptic setup likely favorable for at least
patchy dense fog. Initial fog Thursday evening should focus over
the northeast 1/2 or 1/3 of the CWA and particularly near the
lake, where areas of dense fog may already be oozing inland prior
to sunset on Thursday. As the strong warm front to our south makes
northward progress overnight, fog development looks more
favorable areawide. Flow aloft should remain sufficiently light to
not be much of an impediment to fog development most of the
night. Increasing southerly flow just off the deck towards and
after daybreak Friday should tend to lift the existing low stratus
and fog bank northward. We`ll need to monitor this period for
advisory worthy coverage of sharply reduced visibility. For now,
with the exception of right along the lakefront (areas of fog),
opted for patchy fog mention in the gridded forecast.


Castro

Friday Onward:

On Friday, southwesterly flow will strengthen as a mid-level
jet ejects northeast across the Plains into the Upper Midwest.
This will send a low amplitude shortwave racing northeastward
into the Upper Midwest sometime late Friday morning into early
Friday afternoon, though there is variance in the guidance
regarding the track and strength of this feature. An arc of
showers and isolated to widely scattered thunderstorms
accompanying this feature may impact parts of the region for a
period into Friday afternoon. However, it still appears there
will be a good amount of dry time during the day (more than
implied by the currently high gridded 12 hour PoPs).

Temperatures on Friday are expected to soar well into the 60s
into the low 70s (near record territory for ORD and RFD which is
70 at both sites on Friday) for most through the afternoon as a
surface warm front surges northward across Illinois and Indiana.
However, as is typical this time of year, onshore flow ahead of
this front across far northeastern IL (including parts of Chicago)
may keep conditions much cooler through much of the day until the
warm front clears this area. Patchy fog may also hang on near the
Illinois shore until surface flow turns offshore.

The combination of the very warm temperatures and unseasonably
high dew points into the upper 50s to near 60F, will support an
unstable and strongly sheared warm sector supportive of a
conditional threat of severe thunderstorms Friday afternoon. The
main question at this point is if any of these early afternoon
storms will be able to become surface based near the quickly
approaching warm front before the main focus for them shifts to
our northeast later in the day. If they do become surface based,
then severe storms would be more of threat for a period Friday
afternoon, particularly near the surface boundary. However, at
this time confidence on severe threat with these storms is low.
The currently more likely scenario appears to be the convection
remaining elevated/just north of the front, but it could be close.
Ultimately, it is going to come down to the timing of the
northward frontal surge into northern IL Friday afternoon.

A period of nearly storm free weather could set up for a time
late Friday afternoon and evening due to prominent capping
following this initial impulse, though south-southwesterly winds
do look to become gusty (35+ mph) for a period. Assuming these
capped/primarily dry conditions come to fruition, it will feel
like a warm, slightly muggy, and windy May night for those out
and about. Expect shower and thunderstorm chances and coverage to
ramp up again late Friday night into early Saturday morning in
association with a cold front sweeping eastward across the area.
For the Friday through Friday night period, attempted to provide
approximate temporal details for graphical/tabular/matrix type
depictions of the gridded PoP forecast, in line with general
thinking outlined in this discussion.

The currently unfavorable diurnal timing of the cold front
passage late Friday night into early Saturday does raise questions
as to the threat for organized severe weather with this activity
locally. However, the combined presence of near record warm
temperatures and dew points deep into Friday night within a
strongly sheared kinematic environment certainly will support at
least a conditional risk for some stronger storms capable of
damaging winds late Friday night.

Rain chances will come to an end following the cold frontal
passage on Saturday, at least for a few days. Temperatures will
cool down a bit immediately behind the front Saturday PM, but
generally remain well above average through early next workweek.
For areas that don`t receive much rain in the upcoming stretch,
we`ll need to monitor for elevated fire danger on Sunday due to
mild temps paired with fairly low dew points and gusty southwest
winds. Both next Monday and a part of Tuesday look quite warm
(highs possibly 70+ for a good chunk of the area). Thereafter,
recent medium to long-range ensembles have continued point towards
a stronger cold front passage in the wake of a possible formidable
mid-latitude cyclone with potentially widespread precipitation
mid next week, bringing a return to colder conditions, possibly
accompanied by wind driven accumulating snow somewhere in the
greater region. If this were to happen in our area, it would be
a classic case of March "weather whiplash".

Castro/KJB

&&

.AVIATION /12Z TAFS THROUGH 18Z THURSDAY/...
Issued at 622 AM CST Wed Mar 4 2026

Main Concern:

- Lower flight category trends through the period in BR/fog and
  showers/drizzle, with another period of LIFR to perhaps VLIFR
  possible late tonight into Thursday morning.

The lowest conditions as of 12z stretch from the IL north shore
northwest to the greater RFD area, including ORD at 1SM and
OVC002. Just to the south, MDW and GYY have had much better
conditions. It`s unclear if CIGs will improve to IFR today over
far northeast Illinois, including ORD and DPA. Confidence is
higher in VSBY improving by the mid to late morning. Can`t rule
out spotty sprinkles or drizzle this afternoon at the
terminals, but chances appear too low for formal TAF inclusion.

Setup appears conducive for very low stratus and fog to develop
over southern Lake Michigan tonight and potentially ooze inland
gradually, perhaps as early as this evening. The most likely
timeframe for periodic showers, drizzle, and fog, possibly
dense, looks to be overnight into Thursday morning. Chicago area
terminals appear have a higher potential for dense fog than the
RFD area at this time.

Winds will remain light to moderate from a general east to
northeast direction through Thursday morning.

Castro

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Dense Fog Advisory until 9 AM CST this morning for ILZ003-
     ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013-
     ILZ103.

IN...None.
LM...Dense Fog Advisory until 9 AM CST this morning for Winthrop
     Harbor to Wilmette Harbor IL.

&&

$$

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